The present subject matter relates generally to encoding a frame of video data, and more specifically to encoding the elements of macro-block header based on the values of the elements of the previous header.
Video coding achieves compression by eliminating redundancy in video data. There are two kinds of redundancies in video data: spatial and temporal redundancies. Removal of spatial redundancy and temporal redundancy involves looking within a frame through the use of transform coding techniques and between frames through the use of motion estimation and compensation techniques, respectively.
MPEG4 (“Coding of Moving Pictures and Audio,” ISO/IEC JTC1/SC29/WG11 N3312, March 2000), H.263 (“H.263 Video Coding for Low Bit Rate Communication,” ITU-T Recommendation, 1993), and H.264 (“T. Wiegand, “Working Draft Number 2, Revision 8 (WD-2 rev 8),” JVT-B118r8, ISO/IEC MPEG & ITU-T-T VCEG, Geneva, Switzerland, 29 Jan.-29 Feb. 2002) adopt block-based coding schemes, in which the pictures are divided into smaller units called blocks, which are to be processed one by one in raster-scan order by both the encoder and decoder. A block is defined as a set of 4×4 pixels in H.264, and 8×8 pixels in H.263 and MPEG4. A group of blocks with total size 16×16 is called a macro-block (MB). A number of consecutive MBs are grouped into slices, representing independent coding units to be decoded without referencing other slices of the same frame. Through DCT transformation and quantization, a set of data samples of the block is first linearly transformed and quantized into a set of transform coefficients, resulting in concentrating the energy of input samples into a small number of low-frequency coefficients. Variable length coding (VLC) is adopted for coding resulting residue data.
In low bit-rate video coding, larger quantization parameters are used to give a smaller number of bits spent on residue data. As a result, the header overhead is a dominant factor of yielding the overall bit rates, especially in high-complexity video standards such as H.264. In low bit-rate video coding, it is critical for low-speed network applications (K. Yu, J. Li, C. Shi, and S. Li, “A Novel Model-based Rate-Control Method for Portrait Video Coding,” IEEE Trans. Circuits Syst. Video Technol., Vol. 15, No. 12, December 2005; X. Yang, W. Lin, Z. Lu, X. Lin, S. Rahardja, E. Ong, and S. Yao, “Rate Control for Videophone Using Local Perceptual Cues”, IEEE Trans. Circuits Syst. Video Technol., Vol. 15, No. 4, April 2005) including 20-40 kbps 2.5 G wireless network, 24-64 kbps videophone and 64 kbps ISDN. Recently, watching video on a mobile phone become popular as a majority of mobile phones in the current market offer the capability of viewing mobile video. According to Mobile Video & Statistics in April 2006 (“Mobile Video Research & Statistics,” http://mmaglobal.com/modules/wfsection/article.php?articleid=378), over a half of mobile users watched video on their own mobile phone at least once a week. In Korea, mobile TV was adopted on mobile phone recently. Other countries like the United States will make use of video streaming for mobile TV applications. In the near future, using video over mobile phones will become a common trend among mobile phone users. For those video applications, there is a need for an advanced coding scheme.